1. Field of the Invention
This invention relates to textiles in general, and in particular to an electrically-conductive textile fiber for use in the construction of antistatic fabrics of various kinds.
2. Prior Art
The accumulation of static electricity as a result of the utilization of fabrics is a phenomenon which has commanded the attention of the textile industry for some time. The presence of static is a cause not only of annoyance -- (e.g. items of apparel cling to the body and are attracted to other garments; fine particles of lint and dust are attracted to upholstery fabrics, increasing the frequency of required cleaning; one experiences a jolt or shock upon touching a metal doorknob after walking across a carpet) -- but also of danger (e.g. the discharge of static electricity can result in sparks capable of igniting flammable mixtures such as ether/air, which are commonly found in hospitals, especially in operating rooms). All of these effects are accentuated in atmospheres of low relative humidity.
Of the many proposals for preventing the undesirable buildup of static electricity, the most satisfactory, with respect to their efficiency and permanence, have appeared to be those which comprehend the utilization of fibers possessing electrical conductivity (e.g. metal fibers; fibers coated with electrically-conductive material; fibers containing conductive, block copolymeric materials dispersed therein in the form of long, slender particles; integral fibers having a sheath or core containing electrically-conductive material; and metallic laminate filaments) in combination with common natural or man-made fibers to produce a woven, knitted, netted, tufted, or otherwise fabricated structure, which readily dissipates the static charges as they are generated. Some of the more noteworthy of these methods and structures may be found in U.S. Pat. Nos. 2,129,594; 2,714,569; 3,069,746; 3,288,175; 3,329,557; 3,582,444; 3,582,445; 3,582,448; 3,586,597; 3,590,570; 3,637,908; 3,639,502; 3,729,449; 3,803,453 and 3,823,035; in Webber, "Metal Fibers," Modern Textile Magazine, May, 1966, pp. 72-75; in Belgian Pat. Nos. 775,935 and 790,254; and in French Pat. No. 2,116,106.
Notwithstanding the efficacy of these and similar expedients, they are found lacking in certain important aspects, viz:
The manufacture of metallic fibers of fine denier, especially in the form of monofilaments, is a difficult and costly operation; and since such fibers are quite dissimilar in character from ordinary textile fibers, problems arise in connection with blending and processing, as well as in the hand of the products obtained.
Metallic laminate filaments, on the other hand, do not present blending and processing problems, because of their close similarity to ordinary textile fibers, and the hand of the products obtained is consequently not objectionable. However, the cost of such filaments is high when compared with the natural or man-made fibers with which they are blended.
Textile fiber substrates, the surfaces of which have been coated by vapor deposition or electrodeposition, or by the application of adhesive compositions containing finely divided particles of electrically-conductive material, are in some cases less costly than metal fibers and/or metallic laminate filaments, depending upon the nature of the electrically-conductive material employed and the coating method chosen. However, such coatings are often found lacking in cohesion and adhesion and are frequently too thick to be practicable in some applications -- especially when the nature of the electrically-conductive particulate matter is such that a high concentration thereof is required for satisfactory conductivity. Economy is generally achieved, therefore, only through sacrifices in durability of the conductivity of the fiber.
The extrusion of powdered synthetic polymer/finely divided electrically-conductive material blends directly into filaments, or as distinct coatings on filamentary substrates having the same or different polymeric compositions, is also well known. Unfortunately, these substantially homogeneous blends require a high concentration of the electrically-conductive material. They are generally not readily extruded, if at all, and any filaments and filamentary coatings which are produced therefrom have extremely poor cohesion and adhesion, and are therefore completely lacking in durability.
Filamentary polymer structures containing conductive polymeric materials (e.g. polyalkylene ether - polyamide block copolymers), which are dispersed in the polymer substrate in the form of long, slender particles or layers whose longitudinal axes are substantially parallel to the direction of molecular orientation of the filament, are difficultly obtained in a reproducible form, thereby increasing their cost and/or decreasing the ambit of their utility.
Although they have been shown to provide very beneficial results in most applications, filamentary polymeric structures having either an integral sheath or an integral core comprising electrically-conductive material are somewhat limited in their utility; viz., they are not suitable in applications requiring a very low resistance.
Although multi-component filaments are known in the art (see U.S. Pat. No. 3,531,368, which discloses a multi-component filament comprising a plurality of fine filamentary parts which are continuous along the axis of the filament), and although it is also old to modify one of the components of a multi-component filamentary structure by the introduction of additives such as anti-static agents, including electrically-conductive carbon black (see U.S. Pat. Nos. 2,428,046 and 3,582,448), the present invention as hereinbelow specified and hereinafter defined is not obvious to one of skill in the art, as only the particular combination of elements as recited herein will result in a filament having properties which obviate the deficiencies of the prior art as discussed hereinabove.
Accordingly, it is the primary object of this invention to provide a low-cost, yet durable, electrically-conductive fiber which has reproducible conductive properties over a wide range of conductivities, substantially retains the desirable physical properties of the unmodified polymeric substrate, and presents no problems in the blending and processing thereof with ordinary natural and man-made textile fibers.